1. Field of the Invention
The present invention generally relates to an intrusion detecting device and, more particularly, to the intrusion detecting device for anticrime use for detecting an intruder entering in a guarded or alert region, which is defined in the outdoors of a building such as a factory or a dwelling house, and for generating a warning signal for warning or intimidation for the purpose of driving the intruder away from the guarded region.
2. Description of the Prior Art
The intrusion detecting device of the kind referred to above, which has hitherto been used and is currently used in practice, make use of an infrared detecting sensor of a passive type or a projection type for detecting an intruder and is generally classified into two types. One type is so designed and so configured as to generate the same voice warning repeatedly so long as the presence of an intruder in a guarded or alert region is detected. The other type is so designed and so configured as to drive a buzzer or siren and/or to activate a warning light when the presence of an intruder in a guarded or alert region is detected.
It has, however, been found that those types have their own problems. Specifically, repeated generation of the same voice warning repeatedly such as with the intrusion detecting device of the first mentioned type involves a problem in that a potential intruder can sooner or later apprehend the pattern of operation of the intrusion detecting device and, therefore, the effective intimidation by the voice warning generated repeatedly can not be expected. Where the intrusion detecting device is so designed and so configured to generate a voice message of a kind that is hard-and-fast in an attempt to increase the effectiveness of browbeating, this hard-and-fast voice message is generated even to a unremorseful visitor entering a guarded area, causing such visitor to be set aback and, accordingly, the user of the intrusion detecting device will feel hard to use it.
On the other hand, the intrusion detecting device capable of driving the buzzer or siren and/or activating the warning light with the considerable amount of light is generally set in operation during the nighttime and, accordingly, loud sound and/or flashing light so generated will constitute a nuisance to those living in the neighborhood. Thus, this type of the intrusion detecting device is not well suited for use in the residential district.
Also, an anti-thief security assembly is known which is so constructed as to include two intrusion detecting devices positioned at respective sites distant from and near to a building in order to define associated alert areas. This anti-thief security assembly is known to operate in such a manner that when one of the intrusion detecting devices assigned to monitor the alert area distant from the building detects the presence of an intruder entering into such distant alert area, this intrusion detecting device can generate a voice warning including a moderate message, but when the other intrusion detecting device assigned to monitor the alert area near to the building detects the presence of an intruder entering into such near alert area, this intrusion detecting device can generate a voice warning including a strict message. However, this anti-thief security assembly requires the use of two detecting devices and, correspondingly, two voice sources, resulting not only in complexities in wiring and installation, but also in increase of the cost involved.
In view of the foregoing, the Japanese Laid-open Patent Publication No. 2000-99835, for example, discloses an anti-thief sensor device including a sensor unit and an alarm outputting unit both integrally encased in a single housing. This known anti-thief sensor device is so designed and so configured that when the sensor unit keeps detecting the presence of an intruder entering the alert area, contents of a warning sound generated thereby can vary stepwise with the passage of time subsequent to the time of detection of the intruder. Specifically, with the anti-thief sensor device of the type discussed above, as the time passes subsequent to the time of detection of the intruder, the volume of the warning sound varies from a small blast to a full blast or the outputting cycle of the warning sound varies.
Considering that, when an intruder is kept being detected, the anti-thief sensor device discussed above merely changes the manner of outputting the warning sound only based on the passage of time subsequent to the time of detection of the intruder entering the alert area and that the manner of outputting the warning sound varies in a plurality of predetermined stages, change of the warning sound would be readily apprehended by an intruder. More specifically, since the warning sound varies in the plurality of the predetermined stages regardless of the behavior of the intruder within the alert area, it is possible for the intruder to slyly apprehend that the warning sound would not change from one stage to another in a timing dependent on the behavior of the intruder. Once the intruder so apprehends the way the anti-thief sensor device works, he or she would no longer feel surprised even when the warning sound is generated during his or her subsequent attempt to intrude into the alert area and would be able to stay cool enough to analyze the pattern of change of the generated warning sound, wherefore the anti-thief sensor device would no longer bring a psychological effect on the mind of the intruder. Thus, the known anti-thief sensor device, too, is generally ineffective to browbeat the intruder and, hence, to provide an intended security against possible intruders.